Joke I heard as a kid:
A warship was hunting a submarine and as the sub was surfacing the warship crew dumped green paint on the ocean surface. When the sub's periscope broke the surface the paint coated the periscope, making the capt. think they were still submerged. The sub then kept "surfacing" and continued rising above water. The ship crew then shot the sub with its anti-aircraft guns.
Of course, as a kid it doesn't matter that the paint would coat the periscope lens and make it impossible to look through, or the sub's depth gauges would indicate their depth.
--
